Vapor phase solvent extraction process



Feb. 24, 1.948.v E. F. WADLEY VAPOR PHASE SOLVENT EXTRACTON PRC'ESS Filedv May l5, 1946' mcwmuogm 3,20... coahown .532. coeom.;

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Esci mituo INVENTOR.

BY l l l y f, ATTORNEY."-

Patented Feb. 24, 1948 VAPOR PHASE SOLVENT EXTRACTION PROCESS Edward F. Wadley, Baytown, Tex., assigner, by

mesne assignments, to Standard Oil Developabeth, N. J., a corporation ment Company, Eliz of Delaware Application May 13, 1946, Serial No. 669,347

6 Claims. (Cl. 260-68715) The present application is a continuation-inpart of my copending application Serial No. 547,- 593, filed August l, 1944, which has become abancloned.

The present invention is directed to a process in which a mixture of gaseous or vaporous constituents is scrubbed with a 'liquid capable of taking up one or more of said constituents. \A particular process of this general type to which the present invention is especially applicable is the recovery of butadiene from a mixture of C4 hydrocarbons containing it by scrubbing the mixture with an ammoniacal solution of cuprous acetate.

It has already been proposed to improve the eliiciency of a scrubbing operation of the aforesaid "type by adding to the scrubbing liquid a small amount of another liquid chemically inert t the scrubbing liquid and the gaseous constituents being treated but having high solvent power for such constituents. According to this proposal the amount of added liquid employed is considerably less than 1% because this liquid passes with the scrubbing liquid to a desorption zone wherein the absorbed constituents in the added liquid are removed, together with those from the scrubbing liquid, as a result of which the maintenance of the desired selectivity imposes a restriction on the amount of added liquid which may be employed.

. According to the present invention the efficiency carrier liquid must be immiscible with the scrubbing liquid.

According to the present invention the carrier liquid is preferably used in amounts ranging from about 3 to 5% by volume of the scrubbing medium. Larger amounts, say up to 20%, may be employed, with, however, a corresponding loss in selectivity. It is possible according to the present invention to operate in stages using a large amount of carrier liquid in the rst absorption stage and subjecting the gaseous mixture obtained by desorption of the carrier liquid to a second absorption stage in which from 3 to 5% of carrier liquid is employed. Alternatively, when amounts oi carrier liquid up to 2,0% are employed 2 in the scrubbingv` stage, the carrier liquid, after being separated -from the scrubbing medium, can then be thoroughly mixedwith an amount of fresh scrubbing medium followed by a second separation, the second batch of scrubbing liquid being passed to a desorptionfzone along with the main batch of scrubbing liquid.

The nature of the carrier liquid will depend upon the mixture of the gaseous or vaporous constituents to be treated, las well as upon the scrubbing medium. In the particular process recited above, naphtha having a boiling range from about 350 to 450 F. constitutes a satisfactory car-4 rier liquid. However, other liquids such as kerosene and light gasoil, having suitable boiling point and chemical inertness to the gaseous constituents being treated and sucient solvent power for said gaseous constituents may be ein; ployed as the carrier liquid. V

While an ammoniacal solution of cuprous acetate has been specifically mentioned as a scrub: bing liquid, other liquids which will absorb as by chemical action and desorbby the application of heat, as for example water, ammoniaca] water,

land aqueous solutions of silver nitrate, mercurio cyanide, and cuprous chloride, may also be used for this purpose, l

The present invention may be more clearly understood from the following detailed description ofthe accompanying drawing in which the single ligure is a front elevation in diagrammatic form 4of a type of plant suitable for practice of the present invention. 1

Referring to the drawing in detail, numeral l designates a scrubbing orgextraction tower to an intermediate point of which the gaseous or vapor. ous mixture to be scrubbedcr extracted is introduced through line 2. The scrubbing liquid is injected near the top of thegtower through line 3.

Line 3 is provided with aQ-branch line 4 which Raschig rings, to insure suflicient contact between the gases toy be scrubbed andthe scrubbing me? dium.- y

The extract is discharged from line `6 into a settler l in which two liquid layers are formed,

Athe one being scrubbing medium carrying abv sorbed constituents and the other being carrier liquid carrying absorbed constituents. rIjhe posi` oFFlcE.

tions of the layers will depend upon their respective specic gravity. In the particular operation heretofore referred to in which C4 hydrocarbons containing 'butadiene are scrubbed with an aqueous medium and naphtha is used as a carrier, the scrubbing liquidfforms 'the lower' layer linV settler l' from 'which itis drawn off 'byline-8 and discharged into a desorber 9 in which it is heated to drive oi its absorbed constituents which leave the desorber 9 through line Il): Some 'of these absorbed constituents may be returned to the sorber I4 where it is subjected t'otlie same treat'-r ment as that applied to the scrubbing liquid in the desorber 9. The absorbed constituents liberated from `the carrier 4liquid in stripper I4 may be conducted by line I5 to a'point 'in' the tower 'I below the feed line 2. Alternatively,'they"may be discharged from the "sy-stem 'or fed to a different-system by'way'o outlet I 6,* l l lThe stripped carrier'liquidlis drawn olf from the bottom of stripper 'l'4`by` line I "I Which-conducts it back to feed line It. Since, `in some processes, the carrier liquid picks 'up constituents which arenot `desirable in the system, acetylene polymers in the C4 yhydrocarbon fractionshere- Stofore mentioned, it "may be desirablf': from time totirne to remove part ofthe carrier liquid from thesystem by`wayof line I8. y l

Instead of subjecting the carrier medium to stripping in the manner shown, it may be taken out of the systemby'way oi line VI9 land fed to `the stripping still of the main absorption plant ordinarilyutilized for segregationrof; the C4 `hydrocarbons from other reriery'gases. f

AInthe operation thus fardescribed, it is preferable to limit theamount Vof carrier yliquid employed to from 3 to 5% by 'volume o f the scrubhing '-liquid. As previously `explained; however, larger amounts of carrier liquid may be employed. 'Inthis case itis proposed toremove the C4 hydro l'carbons recovered Vfrom-stripper I4 from the systern illustrated and pass them through an iden- 'tical system in'which from 3 to 5% of carrier liquid Yis` employed. 1

Alternatively, when a relatively llarge 'amount "of carrier liquid is employed, for example about '20% by volume of the scrubbing liquid, the carrier liquid containing absorbed constituents may .be-discharged from line I3 through a-branch Aline 20 `into an incorporator `2I 'to which is also fed "a portion of the desorbed'scrubbing-medium from line" |2 by abranch'line 22. :In'gthis connection lt'will' be advisable to cool the Vdesorbed scrubbing emedium in acooler 23 to atemp'erature suitable 'for Yabsorbti'on 'of the desiredu'const'i'tuents- 4In the lincorpcrator 2'I f the desorbed "scrubbing rne-v iium andthe'fat carrier liquidare thoroughly ntermixed and discharged into a' secondsettler 24. "The scrubbing medium'withdrawn from the bottom of this settler 24d-s 'fed by'wayoi line 25 'back to line 8, While Vthe carrier'liquid is discharged from the upperv part *off the settler Ithrough`-line'26 back to line I3 behind :a valve ticed. In this embodiment the overhead from stripper I4 may be discharged from the system through line I6.

The nature and objects of the present invention having been thus described and illustrated, what is claimed as new and useful and is desired to be secured by Letters Patentis:

1. In a process in which a mixture of gaseous hydrocarbon constituents is scrubbed with an 'aqueous metallic salt solution which is liquid and vcapable of selectively absorbing at least one of said constituents, the steps of adding to the scrubbing liquid at least 3% by volume thereof of a hydrocarbon carrier liquid chemically inert to and immscible with the scrubbing liquid and chemically inert to the gaseous constituents undergoing treatment but having strong solvent -power for said gaseous constituents, separating vto 21 Which-is closed Lwhen lthis'operation "is pr'aqt.

the scrubbing liquid containing absorbed constituents from the carrier liquid containing dissolved constituentsand separately recovering absorbed and dissolved hydrocarbon constituents from said liquids.

l 2. A process for recovering butadiene from a mixture of gaseous hydrocarbons containing it which comprises scrubbing said gaseous mixture with an aqueous metallic salt solution which is liquid and capable of selectively absorbing said butadiene, admixed with at least 3% by volume of a hydrocarbon carrier liquid chemically inert to the scrubbing liquid and immiscible therewith and chemically inert to the gaseous mixture undergoing treatment and having strong solvent power for the constituents of said gaseous mixture, separating the scrubbing liquid containing absorbed butadiene from the carrierliquid containing dissolved constituents and separately recovering absorbed and dissolved butadiene'from said liquids. l 3. A process according to-claim 2 in which the carrier liquid is used in an amount-between about 5% and 20% by volume'of the scrubbing liquid and, after separation from the scrubbing lliquid containing absorbed constituents, `the carrier liquid is admixed with'fresh scrubbing liquid,'the mixture separated into layers and the layers'separately desorbed. f

4. A process according to claim 2 in which'the carrier liquid is a naphtha.

5. A process according to kclaim 2 in-Whichthe "scrubbing liquid is an ammoniacal solution of icupr-ous acetate. Y

6. A method according to `claim 2 in which the scrubbing liquid is an ammoniacal solution of cuprous acetate and the carrier-liquid isv a naphtha. EDWARD F. WADLEY.

`REFERENCES CITED The following references are'of record in fthe 'le or? this patent:

UNITED STAT-'Es PATENTS Number f vName Date l l2.204,903 `McKittrick V Junell, 1940 "2,365,898 `Morrisret al. Dec. 26,1944 2,384,378 Hooker et al. v ,Sept. 4, 1945 

